3/8" NPT Thread Specifications
Complete dimensions for 3/8" NPT (National Pipe Taper) thread per ASME B1.20.1. TPI: 18, Pitch: 0.05556" (1.411 mm). Taper: 1 in 16 on diameter (3/4" per foot).
Thread Dimensions
| Designation | 3/8" NPT |
| Nominal Pipe Size | 3/8" |
| TPI | 18 |
| Pitch | 0.05556" (1.411 mm) |
| Outside Diameter | 0.6750" (17.14 mm) |
| Pitch Diameter at E0 (hand-tight) | 0.61201" (15.545 mm) |
| Pitch Diameter at E1 (wrench makeup) | 0.62701" (15.926 mm) |
| Minor Diameter at E0 | 0.58391" (14.831 mm) |
| Taper Angle | 1.7899° (1:16 taper ratio, 3/4"/ft) |
| Thread Depth (h = 0.8p) | 0.04444" (1.129 mm) |
Values per ASME B1.20.1 Table 1. E0 = hand-tight engagement pitch diameter; E1 = wrench-makeup pitch diameter.
Tap Drill Size
Tap drill: 37/64" (0.5781" / 14.68 mm)
NPT tap drills allow the tap to cut the taper thread. The tap itself creates the taper geometry; drill size provides initial clearance at the large end.
Common Applications
- Plumbing connections
- Gas piping
- Hydraulic fittings
- Pneumatic connections